An important function of a package is to protect its content. It is therefore common that the packaging laminate, which forms the package, contains a gas impermeable barrier layer. An important application of this is within food industry, where one wishes to be able to protect foodstuff from oxygen. Penetrating oxygen may lead to oxidation of certain components of the foodstuff, which may deteriorate its quality and taste and in a worst case lead to that the foodstuff has to be discarded. This protection may be achieved by a gas impermeable or a gas resistant barrier layer. One may also conceive to prevent certain gases from leaking out of the package, e.g. if a foodstuff is packaged with a protective atmosphere such as N2. The packaging material should preferably additionally be flexible and mechanically durable in order to be easy to handle and furthermore preferably not cost too much.
In the environmentally conscious society of today, there is an ambition to abandon non-renewable materials and instead change over to renewable materials. There is therefore a desire to exchange conventional barrier layers of for example metal foils or plastic based on non-renewable polymers, e.g. oil-based polymers, for more environmentally-friendly alternatives.
Packages may for example be produced of a packaging laminate by means of folding and sealing. In this case joints are formed, wherein the interior of the packaging laminate is exposed to the external environment and/or the content of the package.
Since the packages and thereby the barrier layer should function in all kinds of environments, e.g. regarding temperatures and air humidity, it is important that the barrier layer also copes with high air humidities. Previously known material based on renewable raw materials have often had undesired increased gas permeability at high air humidities, especially oxygen permability, but in order to function well as a package, the material must be able to also cope with this.
If a cold package is placed in a warmer environment, e.g. a package taken out from a cold storage to an ordinary room environment, condensate may form on the outside of the package. There is then a risk that the condensate by way of the joints penetrates into the barrier layer and thereby damages the barrier layer. It is therefore desirable that the barrier layer functions well, even when it is exposed to humidity, in order to retain its gas protective function, since renewable barrier layers in general are of a hydrophilic nature and therefore sensitive to humidity. There are also examples of packages which are stored in iced water in order to for example manage cold storage without access to electricity. In this case, the joints are heavily exposed to the surrounding water, since the package is located in the water.
WO 2008103123 A2 by Gröndahl et al describes a polymeric film or coating comprising hemicellulose and at least one component selected from the group consisting of plasticizers, cellulose, and an oligomer or polymer. The polymeric film or coating further comprises at least one additive/reactant increasing the liquid/moisture resistance and mixed with and/or reacting with the hemicellulose and the at least one component before or in conjunction with the forming of the film or coating.
However, even if hemicellulose is commonly present in biomass, the biomass normally goes through a process in order to separate the hemicellulose, such that the hemicellulose thereafter can be used for forming the polymeric film or coating according to WO 2008103123 A2. As an example, it is mentioned on page 5, line 4, that xylan is separated by means of extraction with water and aqueous alkali. Such a separation process step takes time and costs money.
In PCT/EP2008/066148 by Dahlman et al, a method is described for utilizing a wood hydrolysate obtained from a hydrothermal treatment of wood material. The method comprises the steps of providing a wood material and treating it with an aqueous hydrothermal treatment, such that a wood hydrolysate and a wood residue is formed. The hydrolysate comprises oligo- and polysaccharides as a main component of dry matter. The method further comprises the step of separating the hydrolysate into a low molecular and a high molecular fraction. Embodiments disclose films and coatings made of the high molecular fraction.